Routing devices within a network, often referred to as routers, maintain routing information that describe available routes through the network. Upon receiving an incoming packet, the routers examine information within the packet and forward the packet in accordance with the routing information. In order to maintain an accurate representation of the network, routers exchange routing information in accordance with one or more defined routing protocols, such as the Open Shortest Path First (OSPF) or the Intermediate System to Intermediate System (IS-IS).
Multi-protocol Label Switching (MPLS) is a mechanism used to engineer traffic patterns within Internet Protocol (IP) networks. By using MPLS, an ingress device, controller or other path computation element can orchestrate the establishment of a dedicated path through a network, i.e., a Label Switched Path (LSP). An LSP defines a distinct path through the network to carry MPLS packets from an ingress device to a egress device. The ingress device for a given LSP affixes a short label associated with that LSP to packets that travel through the network via the LSP. Routers along the path cooperatively perform MPLS operations to forward the MPLS packets along the established path. LSPs may be used for a variety of traffic engineering purposes including bandwidth management and quality of service (QoS).
A variety of protocols exist for establishing LSPs. For example, one such protocol is the label distribution protocol (LDP) in which label switched routers (LSRs) disseminate labels associated with destinations, referred to generally as forwarding equivalence class (FECs). Another type of protocol is a resource reservation protocol, such as the Resource Reservation Protocol with Traffic Engineering extensions (RSVP-TE), by which dedicated resources along a specified path can be reserved. RSVP-TE uses constraint information, such as bandwidth availability, to compute paths and establish LSPs along the paths within a network. RSVP-TE may use bandwidth availability information accumulated by a link-state interior routing protocol, such as the Intermediate System-Intermediate System (ISIS) protocol or the Open Shortest Path First (OSPF) protocol.
When a failure occurs along an LSP, such as a node failure or a link failure, a router along the LSP that detects the failure typically issues an error message, such as an RSVP PathErr message, indicating to upstream routers that the LSP is unusable. The router also typically originates an OSPF/IS-IS update indicating link failure. In an attempt to avoid the failure, an ingress router for the LSP or other device computes a new path through the network and establishes a new LSP having the same ingress and egress routers but using the different path that attempts to avoid the failed component. In some instances, however, the newly reconfigured LSP may not avoid the failed component that caused the LSP to be unusable, thereby wasting path computation resources and bandwidth in terms of the RSVP-TE messages used to reestablish the LSP.